The invention relates to a method for small-charge blasting, the method comprising drilling with a rock drilling machine a drill hole into a material to be excavated and feeding, after the drilling, at least one cartridge comprising a propellant charge to the drill hole by means of a drilling unit. After this, the drill hole is sealed before the cartridge is ignited. The ignition of a small charge applies a great gas pressure in the borehole, causing fracturing of the material to be excavated.
The invention further relates to a rock drilling unit for small-charge blasting. The drilling unit comprises a feed beam, a rock drilling machine and a drilling tool, which is connected to the rock drilling machine and comprises a channel for feeding a cartridge along the channel into a drill hole. The cartridge is fed to the channel in the drilling tool by means of a feed station.
The field of the invention is defined in greater detail in the preambles of the independent claims.
In small-charge blasting, a cartridge comprising a propellant charge or a similar small charge is arranged in a drill hole. When the cartridge is ignited, a great gas pressure is produced in the drill hole. A great pressure in the drill hole causes controlled cracking in the material to be excavated. Compared to conventional explosion blasting, small-charge blasting provides the advantage that the rock drilling rig need not be transferred away from the drilling site for ignition after the drilling, and thus blasting may be carried out continuously. Furthermore, small-charge blasting does not produce big stress waves, whereby the part of the rock that is not to be broken, stays intact and does not require support. Small-charge blasting is also safer and produces less dust.
U.S. Pat. No. 5,308,149 discloses a drilling unit comprising a rock drilling machine and a feed apparatus for cartridges, which may be indexed on a feed beam. First, a drill hole is drilled by the rock drilling machine, and then the cartridge feed apparatus is indexed at the drill hole for feeding cartridges into the drill hole. The cartridge feed apparatus comprises a massive stemming bar, by which the cartridge is pushed onto the bottom of the drill hole and by which bar the bottom of the drill hole is also sealed. WO 2006/099 637 discloses an alternative arrangement for small-charge blasting. It does not require a separate cartridge feed apparatus in addition to the rock drilling machine, but the cartridges are fed from a feed station in the rock drilling machine to a shank and further through the drill rods to a drill bit, from which they are led to the bottom of the drill hole. A drawback of this solution is that it requires the use of a custom-made rock drilling machine.